A sintered member produced by a powder metallurgical method may be used as various kinds of mechanical parts because it can be formed in nearly a final shape and is suitable for mass production. In addition, it may also be applied to various kinds of sliding parts mentioned above because a special metallic structure can be easily obtained, which cannot be obtained by an ordinarily melted material. That is, in a sintered member produced by the powder metallurgical method, the member may be used as various kinds of sliding parts since a solid lubricating agent can be dispersed in a metallic structure by adding the powder of a solid lubricating agent, such as graphite or manganese sulfide or the like, to raw material powder, and by sintering them under conditions in which the solid lubricating agent remains, (see Japanese Unexamined Patent Application Publication No. Hei04(1992)-157140, No. 2006-052468, No. 2009-155696, etc.).
Conventionally, in a sintered sliding member, a solid lubricating agent such as graphite or manganese sulfide is added in the form of a powder, and remains as it is, and is not solid-solved, during sintering. Therefore, in the metallic structure, the solid lubricating agent is located eccentrically in pores or at particle interfaces of the powder. Since such a solid lubricating agent is not bound to a base in the pore or at the particle interfaces of the powder, it may easily be separated from the base during sliding.
In addition, in a case in which graphite is used as the solid lubricating agent, it is necessary for the graphite to remain as free graphite after sintering and not be solid-solved graphite in the base during sintering. For this reason, sintering temperature should be lower than in a case of a typical iron-based sintered alloy. Therefore, binding between the particles by dispersing of raw material powder may be weakened, and the strength of the base may be decreased.
On the other hand, since the solid lubricating agent such as manganese sulfide does not easily solid-solve in the base during sintering, it is possible to perform sintering at a similar sintering temperature of a typical iron-based sintered alloy. However, the solid lubricating agent that is added in a powdered condition may exist among the raw material powder. Therefore, it may interfere with dispersion among the raw material powder, and the strength of the base may be reduced compared to a case in which the solid lubricating agent is not added. Accompanied by the deterioration of strength of the base, strength of the iron-based sintered member may also be deteriorated, and abrasion may easily be promoted during sliding since durability of the base may be decreased.
In view of such circumstances, an object of the present invention is to provide an iron-based sintered sliding member in which the solid lubricating agent is uniformly dispersed not only in the pores and at the particle interface of the powder, but also inside of the particle of powder, the agent is strongly fixed to the base, sliding property is superior, and mechanical strength is also superior.